BMC’s third sero survey: 36.3% of 10,197 samples have Covid-19 antibodies
The third sero surveillance conducted by Brihanmumbai Municipal Corporation (BMC) in March revealed an overall 36.3% seropositivity in the city, registering an uptick of seropositivity among residents of non-slum areas and a decline in residents of the city’s densely populated slums.
Among the 10,197 samples collected in March, the third serological survey found that 41.6% of the residents of slums had been exposed to the virus while 28.5% of people living in non-slum areas like high rises, chawls and other residential areas, had been exposed to the coronavirus.
A serological survey indicates a population-level prevalence of antibodies against Sar-CoV-2, the virus causing the Covid-19 pandemic. It indicates that a person has been exposed to the virus and has recovered from it, but it does not detect the level of antibodies in the person.
Mumbai, which recorded 5867 new Covid-19 cases on Saturday night taking the total to 622,146 persons infected with Covid-19, conducted 838,500 tests in March. The total number of cases registered by March end was 385,661 with a case fatality rate of 3%.
The first sero surveillance was conducted in the city in July 2020 and the second was conducted a month later, in August.
In the first survey, 57% of samples collected from population residing in slums were seropositive, while in the second survey, 45% were seropositive. In contrast, 16% of samples collected from residents of non-slum areas showed sero positivity in the first survey, which increased to 18% in the second survey.
“It is clear that the percentage of sero positivity in slum areas is decreasing and in non-slum areas the sero positivity is increasing. Considering that currently patients are being found in large numbers from non-slum areas during the second wave of Covid infection, the findings from the Sero survey show that this corresponds to the relevant situation,” the BMC issued a statement on Saturday.
Samples for sero testing non-slum population for are collected by BMC from private laboratories and samples for sero testing in slum population are collected by BMC from municipal laboratories. During the third survey, blood samples were taken from people who have not yet received the Covid-19 vaccine. They were tested for antibodies at BMC’s Molecular Biology Laboratory at Kasturba Hospital.
While 35.02% sero positivity was found among men, 37.12% positivity was found among women.